Numerous attempts to improve the wicking properties and wet strength properties of highly absorbent web structures have been described in the art.
Sigl, et al., U.S. Pat. No. 4,049,764, issued Sept. 20, 1977, disclose an extrusion process for the formation of cellulose fiber webs. Highly absorbent and rapidly wicking filaments and web structures are formed when the extrudate is treated prior to extrusion with a solvent like acetone.
Schmidt, U.S. Pat. No. 4,093,765 issued June 6, 1978, deals with a method of increasing the wet strength of a wet-laid wood pulp fiber web. After drying of the web wet strength additives like urea formaldehyde or melamine formaldehyde are applied to the surface of the web only, to minimize the loss of absorption capacity. In a similar way, Elias, et al., (U.S. Pat. No. 4,233,345 issued Nov. 11, 1980) improved the wet strength of an air laid cellulosic fiber web by lightly spraying with a solution of a coagulating material, e.g. Carbopol 940 after the web is formed.
Tsuchiya, et al., U.S. Pat. No. 4,216,772 issued Aug. 12, 1980, achieved improved structural integrity of a non-woven absorbent structure by admixing therein from 10 to 40% of a hydrophobic thermoplastic fiber and subsequent heat fusion of these fibers. A similar approach was taken by Patience, et al., U.S. Pat. No. 4,219,024 issued Aug. 26, 1980, who provide wet strength properties to an absorbent pad by admixing particles of plastic material which are fused to the fibers in the pad.
U.S. Pat. No. 4,100,324, issued July 11, 1978 to Anderson, et al., discloses the use of hydrophobic thermoplastic fibers of small diameter to increase the strength of cellulose fiber absorbent webs. The thin fibers keep the cellulose fibers together by mechanical entanglement, thus obviating the need of heat fusion.
The common feature of the last five of the cited patents is that they describe an attempt to improve wet strength properties of an absorbent structure by limited application of a relatively hydrophobic wet strength additive. Although loss of absorbency and wicking rates may be minimized by such limited application, the use of hydrophobic materials in absorbent webs to achieve requisite structural integrity inevitably leads to a loss of hydrophilic properties.